1. Field of the Invention
This invention relates methods of and apparatus for the production of wire. Accordingly, it is a general object of this invention to provide new and improved methods and apparatus of such character.
2. Description of the Prior Art
A. Forward
In the production of wire and rod of all shapes and cross sections, the processes of wire drawing, rod rolling and extrusion are the conventional production methods. One or the other of the following two limiting factors plagues each of these processes. By the processes of wire or rod drawing or rolling one can accomplish only small reductions per pass. For larger reductions, successive passes must be followed. The process, however, can then be done as a steady state continuous process with little interruptions. In the process of extrusion, larger reductions can be made in a single pass, but only finite lengths can be extruded and the process is intermittent.
In the search for a truly continuous process, with large reductions per pass, the following four recent processes were proposed and developed:
1. Continuous Extrusion with Viscous Drag by Fuchs -- See: Fuchs, F. J., Wire Jr. 105 October, (1970) PA1 2. Continuous Chamber Extrusion by Fuchs -- See: Fuchs, F. J., and Schmehl, G. L., "Continuous Hydrostatic Extrusion", presented and published, NEL/AIRAPT International Conference on Hydrostatic Extrusion, University of Sterling, Scotland, June 13-15, 1973. PA1 3. Continuous Extrusion Forming by Green -- See: Green, D., "Continuous Extrusion - Forming of Wire Sections", Jr. of the Inst. of Metals, Vol. 100, 1972. PA1 4. Combined Extrusion Drawing for Fine Wire.
Eash process is described briefly, its concept explained and its shortcomings pointed out.
B. Continuous Extrusion with Viscous Drag
The development by Dr. Fuchs of Western Electric, as reported in Wire Jr., 105 (1970), utilizes viscous drag as the motivating force for the extrusion of continuous rod of aluminum or copper. In principle, the liquid passing through a narrow gap between a chamber and a rod drags the rod forward by viscous drag. To maintain flow, a pressure drop prevails between the pressure at an entrance on the back side of the chamber and an exit at the front. Only a small differential pressure can be maintained in each chamber. The difference in pressure between entrance and exit must be below the flow strength of the workpiece material to prevent pinch off. Thus, only low drag and small reductions can be made by the use of a single chamber. In one embodiment, the chambers are piggybacked in tandem to effect large reductions. The highest-pressure chamber is in front, discharging through a passage into a lower-pressure chamber behind it. The discharge from chamber to chamber proceeds, until at the last chamber, the exit pressure is atmospheric. Thus, if the entrance pressure to the first chamber is (say) 200,000 psi, a gradual drop prevails toward the entrance to the chamber at the back. Because of the forward motion of the rod, a small gap around the rod at the walls between chambers does not leak. A rolled or extruded rod could be reduced to final telephone wire size in a single die by a single pass.
This process was apparently abandoned due to poor efficiency. The applicant has calculated the expected power consumed by shear in the liquid itself and has determined that maximum efficiency expected theoretically is in the vicinity of 30%. This 30% efficiency could only be achieved when pressure approaches infinity and the gap between the rod and the chamber approaches zero. Such conditions can not exist in practice. Furthermore, approaching such conditions, the process becomes very unstable and any change in pressure or size of the rod throws the process out of balance.
Thus, due to inefficiency, such process becomes unacceptable for economical production application.
c. Continuous Chamber Extrusion
To avert the shortcomings of the continuous viscous drag extrusion, a continuous segmented chamber extruder, has been developed, as reported by Fuchs, F. J., and Schmehl, G. L., "Continuous Hydrostatic Extrusion", presented and published, NEL/AIRAPT International Conference on Hydrostatic Extrusion, University of Sterling, Scotland, June 13-15, 1973. The continuous chamber is made from matching segments moving in a chainlike manner. Four circumferentially segmented parts form together a short length of the chamber. Longitudinally, many segments form the length of the chamber which is open on both ends. The segments move together parallel to the axis of symmetry of the chamber. They separate at the exit in order to get away from the chamber they formed and then return to the entrance side where they meet again to form the chamber with their matching counter-parts. A die is set at the exit and a rod is fed at the entrance. The rod is squeezed and dragged by the segmented chamber, moving with it towards the die. To enhance the drag, the rod is coated with plastic material before entering the machine. The rod is machined to close tolerances before coating to fit snugly in the chamber. As the rod reaches the die, the drag produces enough pressure to force extrusion through the die. Very little relative motion is expected between the moving chamber and the rod, so that friction losses are minimized.
The motivation mechanism to mobilize the chamber components and the matching of the components requires a high degree of precision. Cleanliness must be maintained to avoid gaps between the matching segments, through which fins from the deforming workpiece might squeeze. Besides being precision made, the mechanism must be highly rigid to produce and withstand the high operating pressures and forces.
Preparation of the raw material to enter the machine (dimensioning and coating) and the watchmakers' precision, combined with massivity demands from the production machine parts and assembly, are the major shortcomings of such machines.
d. Continuous Extrusion Forming
A development by D. Green of the British Atomic Energy Agency, reported at "Continuous Extrusion-Forming of Wire Sections", Jr. of the Inst. of Metals, Vol 100, 1972, employs friction between a workpiece and a tool as the motivating force for continuous extrusion. There, in an explanatory model which describes the principles, a die with a hole is attached to a stationary platen. A top platen with a square groove is mounted over the bottom stationary platen. Together, they form a square chamber with a block closing the left end; the hole in the block is the die opening. The right end of the chamber is open. A round rod is placed in the chamber, touching at the four surfaces. Then, the top platen is made to slide towards the die. Friction from the three sides of the moving platen drags the rod toward the die, where the rod is blocked. Please note that friction from the top platen exceeds and overcomes resistance by friction from the bottom platen. The friction effect on the rod is to upset the rod. The more the rod is upset, the more effective the friction drag becomes. As it comes closer and closer to the die, more contact prevails between the workpiece and the four walls. At the die, the round original rod has already deformed into a square rod. Pressure is high enough to effect an extrusion through the die. As a bonus, the design is made so as to leave a small gap between the die block and the moving platen. Through this gap, a thin chip is discarded, removing the undesired surface of the rod. Standard extruded or rolled stock serves as the workpiece.
When the stationary platen is replaced by a stationary semi-circular member, and the moving platen by a rotating cylindrical tool, a continuous process is established.
The two major factors restricting the efficiency of such process are the redundant work of upsetting the incoming wire and friction losses. The redundant work is due to an upsetting of the original round wire to a square (and then starting from a square rather than a round -- through the die). This work is independent of the attempted reduction. The friction losses in the square channel depend both on friction values and on reduction.
e. Combined Extrusion Drawing for Fine Wire
One of the shortcomings of the process of hydrostatic extrusion is the finite length of an extruded billet. Since the process of wire drawing has the advantage of being a continuous process, the problem of overcoming the batch-interrupted nature of hydrostatic extrusion has long been with us.
When a spool of wire is inserted into a cylindrical chamber, longer runs can be made. Simple spools can be used, and spinning reels and standing reels have been explored at Battelle, as set forth in U.S. Pat. No. 3,328,998, "High Reduction Drawing", By Sabroff, A. M., and Fiorentino, R. J. -- July, 1967, and by Pugh of the National Engineering Laboratories in Scotland, in "The Mechanical Behavior of Materials Under Pressure", FIG. 41 of Chapter 9, "Hydrostatic Extrusion", Elsevier Materials Science Series, 1970, Pugh, H. Ll. D., (Editor). When the extrusion pressure is augmented by a pull, a Robertson process is provided, as described by J. Robertson at "Method of and Apparatus for Forming Metal Articles", British Pat. No. 19,356, October 14, 1893; U.S. Pat. No. 524,504, August 14, 1894. Hundreds of thousands of feet of fine wire, (&lt;0.001 inch), used in the solid state industries, can be spooled and inserted into a 3/4 inch bore chamber to provide very long runs between loadings. Delicate instrumentation to relate chamber pressure to augmenting tension controls is essential for such equipment. Development work along these lines is followed internationally. With present day limited chamber size, only very fine wire production is expected to be economically competitive for this process.
It should be noted that very long wire can be made, but the process is not a truly continuous process.
f. Helical Extrusion
Another process by Green is called Helical Extrusion. There, hydrostatic extrusion is combined with a chip forming process to produce a small gauge wire (of all shapes) directly from an ingot. Reductions of thousands to one are obtained. Because of the involved concept, this prior-art process is not described herein. Very long wire can be made, but the process is not truly continuous. Each ingot is loaded separately.
g. Comparisons of Alternate Processes
In Table I, the alternate possible processes for the production of wire and rod are tabulated vertically. Criteria for the comparison of major characteristics of those processes are listed horizontally, thus obviating the necessity for deliberation. The process of "extrolling" the newly proposed process of this invention, in included.
TABLE I __________________________________________________________________________ COMPARISONS OF ALTERNATE PROCESSES Power Design Dimensional, Property Product Reduction effi- charac- surface & in- Other Process length possible Speed ciency teristics ternal damage comments __________________________________________________________________________ Rolling Un- Small High High Simple, few mov- Poor limited ing parts, rugged Conventional Short Large Moderate Moderate Simple, few mov- Fair extrusion ing parts, rugged Wire Un- Small High High Simple, reliable Good drawing limited Continuous Un- Large Very Excess- Complicated, but Good *Limited only by ability extrusion with limited high* ively few moving parts to collect product viscous drag poor Continuous Un- Large* Moderate Claimed Complicated, many Good *Reported 300 to 1 in chamber limited to high highest moving parts** copper at up to 300,000 extrusion in trade psi pressure **Requires high precision combined with rigidity & many moving parts that must fit one to each other Continuous Un- Large High Fair to Simple, few mov- Good extrusion forming limited poor ing parts, rugged Combined hydro- Very Moderate Highly Poor Complicated and Very static extrusion long to large re- but not delicate good and drawing for stricted a factor fine wire Helical Very Sky Moderate- ? Complicated, but Good extrusion long high ly high rugged "Extrolling" Un- Moderate- High Fair to Simple, few mov- Good limited ly high high ing parts, rugged __________________________________________________________________________